Chrysotile asbestos fibers were administered via inhalation to mice for three days. Bone marrow cellularity, pleuripotent stem cells and macrophage granule progenitors were quantitated for twelve months following exposure. Bone marrow parameters were depressed at all time periods. Ultrastructural examination was used to confirm the deposition of the fibers in the centriacinar region of the lung. These results were published in 1984.